A. Technical Field
The present invention relates to the field of measuring network responses in the time-domain and, more particularly, to systems, devices, and methods of measuring complex impedance of test samples, including biomedical test samples.
B. Background of the Invention
A number of instruments in the biomedical and fitness area, such as blood glucose meters, respiration monitors, and galvanic skin response meters are designed to measure impedance or conductance of a biological sample in order to generate diagnostic and other useful information. By measuring the AC impedance of a person's skin, for example, a galvanic skin response can be obtained from which an estimate of a person's hydration level may be made.
More complicated devices that, for example, measure the impedance of a blood sample on a blood glucose measurement strip that contains chemicals require enhanced accuracy and perform relatively complicated AC impedance measurements from which diagnostic information may then be extracted. Some existing methods utilize an analog down-conversion process that necessitates a relatively high number of circuit components. However, this process is prone to channel mismatch and low accuracy caused by gain mismatch issues.
Other existing approaches apply Fast Fourier Transform (FFT) methods which utilize a rather power-hungry conversion process to feed large amounts of data samples through an analog-to-digital converter followed by a sophisticated post-processing algorithm. From the system response a transfer function is then calculated in order to extract magnitude and phase information from which then the complex impedance of a test sample is determined.
With the advent of portable electronics, however, the demand for lower power portable medical instrumentation with extended battery life is becoming increasingly important. Unfortunately, the high price of accuracy paid in the form of complicated circuitry that requires relatively high power and operates with inefficient algorithms is incompatible with the goal of modern portable and wearable instruments. What is needed are systems and methods to overcome the above-described limitations.